[Illustration: Fig. 63.--The Improved Ross-Zentmayer Model.]
The base or foot of the Ross-Zentmayer instrument is made in one piece. Preference must be given to the double pillar support, as this is firmer, and allows the sub-stage to swing free while the microscope is in a vertical position, as in working with fluid preparations. The sub-stage is provided with screws for centring, and, when determined, secured by a clamping screw.
The sub-stage, with its apparatus in place, can be instantly removed, by being drawn out sideways, so as to use the mirror alone, which is a great convenience.
The mechanical movements of this instrument are perfect, and well adapted to their purpose.
Messrs. Ross have other typical forms of microscopes. Their _“New Industrial” Microscope_, for the use of farmers, horticulturists, textile and other trades, for the examination of produce and raw materials, is a surprisingly cheap one, and deserving of commendation. The great utility of microscopical research to purposes of advanced agriculture is fully recognised, and a less costly instrument than that usually supplied for more complex investigations was much needed. It is provided with a broad square stage for the purpose of receiving a glass dish to contain liquids or manifold objects, and which may be moved on the stage to bring the various particles under observation. A fitting beneath the stage carries a plate with diaphragm apertures for modifying the light, and as seeds, textile fibres, and other opaque objects form a large portion of those to be examined, this sub-stage plate has a space between the perforations which, when brought into position, provides a dark ground by preventing the passage of light from underneath. A condensing lens is, however, provided for the better lighting of opaque objects. Here we have a microscope which combines efficiency with stability, while its very simplification allows of a really good and effective instrument for the small sum of £3 3_s._
[Illustration: Fig. 64.--Ross’s “New Industrial” Microscope.]
Messrs. Beck have adopted what may be termed a rival system of fine adjustment in their modern microscopes. The short lever and screw applied externally to the body tube is peculiar, I may say, to the Ross-Jackson system, and was originally devised to allow of the body tube being supported somewhat more firmly on the limb. This change had its merits fully realised in the early microscopes of Smith and Beck. To their successors, R. & J. Beck, the microscope owes much, and very many important improvements, while all their instruments and accessories are excellent examples of good workmanship and finish. In their _Pathological Microscope_ we have a movement originally found in Tolles’ microscopes: a vertical disc, by which the centre can be raised or depressed to correspond with the thickness of the slide. The stage can also be brought into an inverted position by rack and pinion. Their fine adjustment has been greatly improved, as we shall presently see, whereby it has been made more sensitive and delicate of adjustment. The general construction of their microscopes as a rule possess the following advantages: the stands are strong, firm, and yet not too light or too heavy, the instruments cannot alter from the position in which they are placed, as, unfortunately, will occasionally happen when joints work loose; in every position the heavier part of the stand maintains the centre of gravity.